Field of the Invention
The present invention relates to an inspection apparatus which makes use of a pattern recognition technique. More particularly, the present invention is concerned with an apparatus which picks up image of an object having a geometric pattern constituted by dark and bright portions formed in accordance with a design data, e.g., a mask or reticle used in the production of semiconductor integrated circuits, and which detects any defect in the pattern by comparing data corresponding to the image with the design data.
2. Related Background Art
An apparatus of the kind described above is disclosed in the specification of U. S. Pat. No. 4,589,139. In this known apparatus, characteristics of pattern edges are extracted both from the image data and the design data and the real pattern on the object is judged to be defective when both data do not have common characteristics. The judgment is conducted on the basis of an assumption that the edges of the real pattern are roughly approximated by line edges which extend in x- and y-directions and line edges which extend at 45.degree. C. to x- and y-directions, and bend edges are extracted as edge characteristics, employing a plurality of templates. The apparatus has a problem in that it may judge any defective real pattern as being acceptable or vice versa, when the real pattern has edges of random angles or directions other than those mentioned above. The current demand for higher scale of integration of semiconductor integrated circuits naturally leads to a greater number of circuit patterns of random angle or direction. This tends to impair the precision of inspection by the known apparatus.
Any defect in the pattern on a mask or a reticle is correctable by a suitable repair means. The repairing cost, however, is increased in proportion to the number and the sizes of the defects. The defect data obtained through the known inspection apparatus includes only edge characteristics. Thus, it has been impossible to know the sizes of the defects, although the number of the defects is detectable. In consequence, there has been no way for precisely estimating the cost required for the repair.